Worm reducer

Abstract

To provide a worm reduction gear which can suppress the size enlargement of a housing in an installation point of a spring which energizes a tip part of a worm toward a worm wheel side, can easily secure a degree of freedom of the design of the spring, and can suppress the operation torque of the worm.SOLUTION: A holder 19 has a holder cylinder part 35 in which a support bearing 20 is arranged inside a radial direction, and a spring holding part 36 arranged in a position adjoining one side in a first direction being an axial direction of a worm accommodation part 23 with respect to the holder cylinder part 35. A plate spring 21 has a main body plate part 47 attached to the spring holding part 36, and arranged at one side in the first direction with respect to the support bearing 20, and a push-press plate part 48 connected to the main body plate part 47, and push-pressing a portion located at a side apart from a worm wheel 17 on the basis of an elastic force generated at the main body plate part 47 related to a second direction being an energization direction of a tip part of a worm 18 by the plate spring 21 out of an external peripheral face of an outer ring 33.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a worm reduction gear incorporated in, for example, an electric power steering device. [Background technology]

[0002] 2. Description of the Related Art Electric power steering devices that use an electric motor as an auxiliary power source are widely used as devices for reducing the force required to operate the steering wheel when applying a steering angle to the steered wheels of an automobile.

[0003] Electric power steering devices are roughly classified into different structures depending on the mounting position of the electric motor.Specifically, various structures have been proposed, such as a column assist type that applies auxiliary power to a steering shaft rotatably supported inside the steering column, a pinion assist type that applies auxiliary power to a pinion shaft that is the input shaft of a steering gear unit, and a dual pinion type that provides an auxiliary power to a pinion shaft separate from the pinion shaft that is the input shaft of the steering gear unit.

[0004] In either structure, auxiliary power from an electric motor is applied via a reduction gear to a shaft member that rotates or moves linearly in response to the operation of a steering wheel. Worm reduction gears are widely used as such reduction gears. The worm reduction gear that constitutes the electric power steering device includes a worm that is rotationally driven by an electric motor and a worm wheel that meshes with the worm.

[0005] 19 shows an example of a conventional structure of a worm reducer described in Japanese Patent No. 4381024 (Patent Document 1). A worm reducer 100 includes a housing 101, a worm wheel 102, and a worm 103.

[0006] The housing 101 has a wheel accommodating portion 104 and a worm accommodating portion 105 whose central axis is skewed with respect to the central axis of the wheel accommodating portion 104 and whose axially intermediate portion opens into the wheel accommodating portion 104.

[0007] The worm wheel 102 has wheel teeth 106 on its outer circumferential surface, and is supported coaxially around a rotating shaft 107 that is supported rotatably inside the wheel accommodating portion 104 .

[0008] The worm 103 has worm teeth 108 that mesh with the wheel teeth 106 on the outer peripheral surface of an axially intermediate portion. The worm 103 is rotatably supported inside the worm accommodating portion 105 by two ball bearings 109a and 109b at two axial positions sandwiching the worm teeth 108. Of the two ball bearings 109a and 109b, the outer ring of the ball bearing 109a on the tip side of the worm 103 (the right side in FIG. 19) is press-fitted into a holder 110 that is fitted and fixed inside the inner end portion of the worm accommodating portion 105. The inner ring of the ball bearing 109a is clearance-fitted around a large diameter portion 111 provided in a portion of the worm 103 that is located on the tip side of the worm teeth 108, via a synthetic resin bush 112. That is, the inner ring of ball bearing 109a is fitted without rattle onto bushing 112 which is loosely fitted onto large diameter portion 111 of worm 103. The outer ring of ball bearing 109b on the base end side (left side in FIG. 19) of worm 103 is press-fitted into the opening of worm accommodating portion 105, and the inner ring of ball bearing 109b is fitted onto the base end of worm 103. An output shaft of electric motor 113 is connected to the base end of worm 103 so as to be able to transmit torque. That is, worm 103 can be rotated by electric motor 113.

[0009] In the worm reduction gear 100, unavoidable backlash exists at the meshing portion between the wheel teeth 106 and the worm teeth 108 due to dimensional errors and assembly errors of the components that make up the worm reduction gear 100. Due to the existence of this backlash, an unpleasant teeth rattle may occur at the meshing portion when changing the direction of rotation of the steering wheel. In the illustrated example, the tip end of the worm 103 is elastically biased toward the worm wheel 102 in order to suppress the occurrence of such teeth rattle.

[0010] That is, the base end of the worm 103 is supported by a ball bearing 109b having a radial gap with respect to the worm housing portion 105 so as to be able to oscillate slightly. An annular gap exists between the outer peripheral surface of the large diameter portion 111 of the worm 103 and the inner peripheral surface of the bush 112 over the entire circumference. A pad 114 is fitted onto the tip end of the worm 103, and a torsion coil spring 115 is installed between the pad 114 and the holder 110. The torsion coil spring 115 elastically presses the pad 114 toward the worm wheel 102 in a second direction (the up-down direction in FIG. 19) in which the worm 103 moves toward or away from the worm wheel 102, thereby elastically biasing the tip end of the worm 103 toward the worm wheel 102 in the second direction (the down direction in FIG. 19). This reduces backlash between the wheel teeth 106 and the worm teeth 108, thereby reducing the occurrence of teeth rattle noise.

[0011] Also, as described in Japanese Patent No. 6108358 (Patent Document 2), Japanese Patent No. 6313969 (Patent Document 3), etc., and conventionally known, a worm reducer having a structure for suppressing backlash between the wheel teeth and the worm teeth by elastically biasing the tip of the worm toward the worm wheel is known in which a biasing spring is arranged so that the entirety of the biasing spring is overlapped radially outwardly with respect to a rolling bearing fitted onto the tip of the worm. In this structure, the biasing spring elastically biases the tip of the worm toward the worm wheel via the rolling bearing. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Patent No. 4381024 [Patent Document 2] Patent No. 6108358 [Patent Document 3] Patent No. 6313969 Summary of the Invention [Problem to be solved by the invention]

[0013] In the structure described in Japanese Patent No. 4381024, the tip of the worm 103 is supported by rolling on the ball bearing 109a, and is also supported by sliding on the inner peripheral surface of the pad 114 pressed against the outer peripheral surface of the ball bearing 109a. Therefore, the operating torque of the worm 103 increases by the amount of the frictional force acting on the part that is supported by sliding. There is room for improvement.

[0014] In the structures described in Japanese Patent No. 6,108,358 and Japanese Patent No. 6,313,969, there is no pad that is pressed against the outer peripheral surface of the tip of the worm in sliding contact, and as a result, the operating torque of the worm can be reduced.

[0015] However, in the structures described in Japanese Patent Nos. 6108358 and 6313969, the entire biasing spring is disposed radially outwardly overlapping the rolling bearing fitted onto the tip of the worm, which causes a problem that the worm accommodating portion of the housing becomes larger in diameter at the installation location of the spring, or if an attempt is made to prevent the worm accommodating portion from becoming larger in diameter, the installation space for the spring becomes narrower, reducing the degree of freedom in designing the spring.

[0016] The present invention aims to provide a worm reducer that can prevent the housing from becoming larger in diameter at the installation location of a spring that urges the tip of the worm toward the worm wheel, can easily ensure freedom in the design of the spring, and can reduce the operating torque of the worm. [Means for solving the problem]

[0017] A worm reducer according to one aspect of the present invention includes a housing, a worm wheel, a worm, a holder, a support bearing, and a leaf spring.

[0018] The housing includes a wheel receiving portion, and ,shaft The directional intermediate portion has a worm receiving portion that opens into the wheel receiving portion.

[0019] The worm wheel has wheel teeth on its outer circumferential surface, and is rotatably supported inside the wheel accommodating portion.

[0020] The worm has worm teeth on its outer circumferential surface that mesh with the wheel teeth, and is rotatably supported inside the worm accommodating portion.

[0021] The holder is configured in an annular shape, a tip end portion of the worm is inserted into the radially inner portion of the holder, and the holder is fitted and fixed within the worm accommodating portion.

[0022] The support bearing is a rolling bearing having an inner ring and an outer ring, and is disposed between the outer peripheral surface of the tip of the worm and the inner peripheral surface of the holder with a radial gap between the outer peripheral surface of the outer ring and the inner peripheral surface of the holder. A cylindrical bush may be disposed between the outer peripheral surface of the outer ring and the inner peripheral surface of the holder.

[0023] The leaf spring is attached to the holder, and elastically biases the tip end of the worm toward the worm wheel via the support bearing.

[0024] The holder has a holder cylindrical portion in which the support bearing is arranged radially inside, and a spring retaining portion arranged adjacent to one side of the holder cylindrical portion in a first direction, which is the axial direction of the worm accommodating portion.

[0025] The leaf spring has a main body plate portion attached to the spring retaining portion and positioned on one side of the support bearing in the first direction, and a pressing plate portion connected to the main body plate portion and pressing a portion of the outer peripheral surface of the outer ring that is located farther from the worm wheel in a second direction, which is the direction in which the leaf spring biases the tip of the worm, based on elasticity generated in the main body plate portion.

[0026] In one embodiment of the worm reducer of the present invention, a cylindrical bushing is fitted into the inner surface of the holder tube portion in a state where radial displacement is prevented, and is fitted outwardly into the outer peripheral surface of the outer ring with a radial gap therebetween.

[0027] In one embodiment of the worm reducer of the present invention, the bush has a bush spring portion adjacent to the outer ring in a third direction perpendicular to both the first direction and the second direction, the bush having a smaller radial thickness than adjacent portions on both circumferential sides, the radial inner surface of the bush spring portion is in contact with the outer peripheral surface of the outer ring, and a gap exists radially outwardly of the bush spring portion to allow the bush spring portion to elastically deform radially outward.

[0028] In the worm reduction gear according to one aspect of the present invention, one side in the first direction is a base end side of the worm.

[0029] A worm reducer according to one aspect of the present invention includes a second leaf spring for preventing a tip end of the worm from being displaced relative to the holder in a third direction perpendicular to both the first direction and the second direction. The second leaf spring has two elastic plate portions that elastically hold the outer ring from both sides in the third direction. Effect of the Invention

[0030] According to one embodiment of the worm reducer of the present invention, the housing does not need to be large in diameter at the installation location of the leaf spring that biases the tip of the worm toward the worm wheel, it is easier to ensure freedom in the design of the leaf spring, and the operating torque of the worm is reduced. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 is a diagram showing an electric power steering device incorporating a worm reduction gear according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing a part of an electric power steering device incorporating the worm reduction gear of the first example. [Diagram 3] FIG. 3 is a cross-sectional view taken along line AA of FIG. [Figure 4] Figure 4(a) is a view of the worm wheel and worm that constitute the first example of an orthogonal type worm reducer, viewed from a direction perpendicular to both the central axis of the worm wheel and the central axis of the worm, and Figure 4(b) is a view of the worm wheel and worm that constitute an oblique type worm reducer, viewed from a direction perpendicular to both the central axis of the worm wheel and the central axis of the worm. [Diagram 5] FIG. 5 is an enlarged view of the upper right portion of FIG. [Figure 6] FIG. 6 is a view of the biasing mechanism (holder, support bearing, bushing, and leaf spring) of the first example, viewed from the right side of FIG. [Figure 7] FIG. 7 is a view of the biasing mechanism of the first example as viewed from the left side of FIG. [Figure 8] FIG. 8 is a view of the biasing mechanism of the first example as viewed from the left side of FIG. [Figure 9] FIG. 9 is an exploded perspective view of the biasing mechanism of the first example, as viewed from the right side of FIG. [Figure 10] FIG. 10 is an exploded perspective view of the biasing mechanism of the first example, as viewed from the left side of FIG. [Figure 11] FIG. 11 is a diagram showing a second embodiment of the present invention, which corresponds to FIG. [Figure 12] FIG. 12 is a view of the biasing mechanism of the second example as viewed from the left side of FIG. [Figure 13] FIG. 13 is an exploded perspective view of the biasing mechanism of the second example, as viewed from the left side of FIG. [Figure 14] FIG. 14 is a view corresponding to FIG. 12 and showing a biasing mechanism of the third example. [Figure 15] FIG. 15 is a view corresponding to FIG. 13 and showing a biasing mechanism of the third example. [Figure 16] FIG. 16 is a view corresponding to FIG. 12 and showing a biasing mechanism of the fourth example. [Figure 17] FIG. 17 is a cross-sectional view taken along line BB of FIG. [Figure 18] FIG. 18 is a view corresponding to FIG. 13 and showing a biasing mechanism of the fourth example. [Figure 19] FIG. 19 is a cross-sectional view showing an example of a conventional structure of a worm reduction gear. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] [First Example of Implementation] A first embodiment of the present invention will be described with reference to Figures 1 to 10. In this embodiment, a worm reduction gear according to one aspect of the present invention is applied to a pinion-assist type electric power steering device. However, the worm reduction gear of the present invention can be widely applied to column-assist type and dual-pinion type electric power steering devices, and various mechanical devices other than electric power steering devices.

[0033] The electric power steering device 1 of this example includes a steering wheel 2, a steering shaft 3, a steering column 4, a pair of universal joints 5a, 5b, an intermediate shaft 6, a steering gear unit 7, and an electric assist device 8.

[0034] The steering wheel 2 is supported and fixed to the rear end of the steering shaft 3. The steering shaft 3 is rotatably supported inside a steering column 4 supported on a vehicle body. The front end of the steering shaft 3 is connected to a pinion shaft 9 of a steering gear unit 7 via a rear universal joint 5a, an intermediate shaft 6, and a front universal joint 5b. Therefore, when the driver rotates the steering wheel 2, the rotation of the steering wheel 2 is transmitted to the pinion shaft 9 via the steering shaft 3, the pair of universal joints 5a and 5b, and the intermediate shaft 6. The rotation of the pinion shaft 9 is converted into a linear motion of a rack shaft 10 of the steering gear unit 7 meshed with the pinion shaft 9. As a result, a steering angle according to the amount of rotation of the steering wheel 2 is applied to the pair of steered wheels. The electric assist device 8 applies auxiliary power generated by an electric motor 15 as a power source to the pinion shaft 9. As a result, the force required for the driver to rotate the steering wheel 2 is reduced.

[0035] The steering gear unit 7 includes a housing 11 supported and fixed to the vehicle body, a rack shaft 10, and a pinion shaft 9. The housing 11 includes a rack accommodating section 12 extending in the vehicle width direction, and a pinion accommodating section 13 connected to one axial side of the rack accommodating section 12 (the right side in FIG. 1). The central axis of the pinion accommodating section 13 is in a twisted position with respect to the central axis of the rack accommodating section 12. The internal space of the pinion accommodating section 13 communicates with the internal space of the rack accommodating section 12. The rack shaft 10 is supported inside the rack accommodating section 12 so as to be capable of only axial movement (vehicle width direction). The pinion shaft 9 is supported inside the pinion accommodating section 13 so as to be capable of only rotation. The pinion shaft 9 has pinion teeth on the outer circumferential surface of a tip half (lower half in FIG. 2) (not shown) located inside the pinion accommodating section 13. A base end (upper end in FIG. 2) of the pinion shaft 9 protrudes outside the housing 11 and is connected to the front universal joint 5b. The rack shaft 10 has rack teeth that mesh with pinion teeth of the pinion shaft 9 on a part of the circumferential direction of the outer circumferential surface of one axial side portion (right side portion in FIG. 1) not shown that is disposed inside the rack accommodating portion 12. In this example, the pinion shaft 9 and the rack shaft 10 intersect obliquely when viewed from a direction perpendicular to both the pinion shaft 9 and the rack shaft 10.

[0036] The electric assist device 8 includes a worm reduction gear 14 and an electric motor 15. The electric assist device 8 is configured to transmit the rotation of the electric motor 15 to the pinion shaft 9 after reducing the speed by the worm reduction gear 14.

[0037] The worm reducer 14 includes a housing 16, a worm wheel 17, a worm 18, a holder 19, a support bearing 20, and a leaf spring 21.

[0038] The housing 16 includes a wheel receiving portion 22, and ,shaft The worm receiving portion 23 has a middle portion in the direction thereof that opens into the wheel receiving portion 22 .

[0039] That is, the central axis of the wheel accommodating portion 22 and the central axis of the worm accommodating portion 23 are disposed at positions twisted relative to each other. Also, an axially intermediate portion of the worm accommodating portion 23 is integrally connected to one circumferential location of the radially outer end portion of the wheel accommodating portion 22, and the internal space of the worm accommodating portion 23 communicates with the internal space of the wheel accommodating portion 22 through this connected portion. In this example, the worm accommodating portion 23 is configured in a cylindrical shape with a bottom, and specifically, the axial tip (right end in FIG. 3) is closed and the axial base end (left end in FIG. 3) is open.

[0040] In this example, the wheel accommodating portion 22 is coaxially and integrally connected to an axially intermediate portion of the pinion accommodating portion 13 that constitutes the housing 11 of the steering gear unit 7. The internal space of the wheel accommodating portion 22 communicates with the internal space of the pinion accommodating portion 13.

[0041] The worm wheel 17 has wheel teeth 24 on its outer circumferential surface, and is rotatably supported inside the wheel accommodating portion 22. In this example, the worm wheel 17 is fitted and fixed to the outside of the pinion shaft 9 at an axially intermediate portion.

[0042] The worm 18 has worm teeth 25 that mesh with the wheel teeth 24 at the axially intermediate portion of its outer circumferential surface, and is supported rotatably inside the worm accommodating portion 23 .

[0043] In this example, the base end (the left end in Figure 3) of the worm 18 is supported in the worm accommodating portion 23 so as to be capable of slight swinging displacement, and is connected to the output shaft 26 of the electric motor 15 so as to be capable of transmitting torque.

[0044] For this purpose, in this example, the worm 18 has a female spline portion 27 on the inner peripheral surface of the base end portion. The electric motor 15 is connected and fixed to the axial base end portion of the worm housing portion 23 by screwing, with the output shaft 26 of the electric motor 15 being arranged coaxially with the worm housing portion 23. The female spline portion 27 of the worm 18 and a male spline portion 28 provided on the outer peripheral surface of the output shaft 26 of the electric motor 15 are spline-engaged. This connects the base end portion of the worm 18 and the output shaft 26 of the electric motor 15 in a manner that allows torque transmission and allows the worm 18 to oscillate slightly. The base end portion of the worm 18 is supported by a ball bearing 29 having a radial gap with respect to the worm housing portion 23, allowing slight oscillating displacement.

[0045] In this example, the outer peripheral surface of the tip end of the worm 18 is configured as a stepped cylindrical surface. That is, as shown in Fig. 5, the outer peripheral surface of the tip end of the worm 18 has a small diameter cylindrical surface portion 30 that configures the tip end side portion, and a large diameter cylindrical surface portion 31 that configures the base end side portion and has a larger diameter than the small diameter cylindrical surface portion 30.

[0046] As shown in FIG. 4(a), the worm reduction gear 14 of this embodiment has a central axis O of the worm wheel 17 when viewed from a second direction (the vertical direction in FIGS. 3 and 5) which is the biasing direction of the tip portion of the worm 18 by the leaf spring 21 described later. 17 and the central axis of the worm 18 (the central axis of the output shaft 26 of the electric motor 15) O 18 However, in the present invention, as shown in FIG. 4(b), the central axis O of the worm wheel 17 is perpendicular to the axis of the worm wheel 17 when viewed from the second direction. 17 and the central axis O of the worm 18 18The present invention can also be applied to an oblique type worm reducer in which the pinion shaft and the rack shaft intersect obliquely, i.e., at an acute angle. If the present invention is applied to an oblique type worm reducer, it becomes possible to arrange the central axis of the electric motor constituting the electric assist device parallel to the rack shaft, even if the pinion shaft and the rack shaft intersect obliquely when viewed from a direction perpendicular to both the pinion shaft and the rack shaft constituting the steering gear unit. This improves the layout flexibility when the electric power steering device is mounted on the vehicle body. Such an effect can be obtained not only in a pinion-assist type electric power steering device as in this example, but also in a dual pinion type electric power steering device.

[0047] In the worm reducer 14 of this example, as shown in Figures 3 and 5, a holder 19, a support bearing 20, and a leaf spring 21 are arranged between the outer peripheral surface of the tip of the worm 18 and the inner peripheral surface of the tip of the worm accommodating portion 23.

[0048] The holder 19 is formed in an annular shape, the tip of the worm 18 is inserted into the radially inner side, and the holder 19 is fitted and fixed in the worm accommodating portion 23. The support bearing 20 is a rolling bearing having an inner ring 32 and an outer ring 33, and is disposed between the outer peripheral surface of the tip of the worm 18 and the inner peripheral surface of the holder 19, with a radial gap being interposed between the outer peripheral surface of the outer ring 33 and the inner peripheral surface of the holder 19. The leaf spring 21 is assembled to the holder 19, and elastically biases the tip of the worm 18 toward the worm wheel 17 via the support bearing 20. This suppresses backlash at the meshing portion between the wheel teeth 24 and the worm teeth 25.

[0049] 5 to 10, the holder 19 has a holder tubular portion 35 on the radially inner side of which the support bearing 20 is disposed, and a spring retaining portion 36 disposed adjacent to the holder tubular portion 35 on one side (the right side in FIGS. 3 and 5) in a first direction (the left-right direction in FIGS. 3 and 5) which is the axial direction of the worm accommodating portion 23. The holder 19 is preferably made of a material having sufficient strength and rigidity, such as a metal material or a synthetic resin mixed with a reinforcing material as necessary.

[0050] In this example, the holder tube portion 35 is configured in a cylindrical shape. The holder tube portion 35 has a recess 37 that opens radially inward and to the other side in the first direction (the left side in FIGS. 3 and 5 ) at one location in the circumferential direction on the inner circumferential surface, specifically, at an end of the inner circumferential surface that is closer to the worm wheel 17 in the second direction. In this example, in order to fix the holder 19 to the worm accommodating portion 23, the outer circumferential surface of the holder tube portion 35 is fitted into the inner circumferential surface of the worm accommodating portion 23 by interference fit (press fit).

[0051] In this example, the holder 19 further includes a circular holder side plate portion 38 extending radially inward from one end of the holder cylindrical portion 35 in the first direction. The holder side plate portion 38 has a notch 39 that opens radially inward and on both axial sides at one location in the circumferential direction, specifically, at the end on the side farther from the worm wheel 17 in the second direction.

[0052] When carrying out the present invention, the spring retaining portion constituting the holder may have any shape as long as the leaf spring can be properly attached in a state in which the worm reduction gear is assembled.

[0053] In this example, the spring holding portion 36 protrudes toward one side in the first direction from a radially inner portion of the holder side plate portion 38. As shown in Fig. 6 and Fig. 9, the spring holding portion 36 has a substantially arc shape centered on the central axis of the holder 19 when viewed from the first direction.

[0054] That is, the spring holding portion 36 protrudes toward one side in the first direction from a portion extending from an end portion of the radially inner portion of the holder side plate portion 38 that is closer to the worm wheel 17 in the second direction to an end portion on one side (the back side in the front-back direction in Figs. 3 and 5, the right side in Fig. 6) in the third direction (the front-back direction in Figs. 3 and 5) that is a direction perpendicular to both the first direction and the second direction. Note that since the worm reducer 14 in this example is an orthogonal type worm reducer, the third direction coincides with the axial direction of the worm wheel 17. In addition, when the present invention is implemented, the circumferential length of the spring holding portion can be set to any length as long as a leaf spring can be attached to the spring holding portion and the leaf spring attached to the spring holding portion can elastically bias the tip portion of the worm toward the worm wheel side via the support bearing.

[0055] In this example, the spring holding portion 36 is composed of a partial cylindrical portion 40 having a substantially partial cylindrical shape protruding from a radially inner portion of the holder side plate portion 38 toward one side in the first direction, and a flange portion 41 protruding radially outward from an end portion of the partial cylindrical portion 40 on one side in the first direction. In this example, a circumferential end portion 42 of the partial cylindrical portion 40 located on the side closer to the worm wheel 17 in the second direction is configured in a flat plate shape extending in the third direction. The portion of the partial cylindrical portion 40 other than the circumferential end portion 42 is configured in a partial cylindrical shape. However, the partial cylindrical portion may be configured in its entirety in a partial cylindrical shape.

[0056] In this example, the support bearing 20 is configured as a ball bearing, as shown in Figures 5, 6, and 8 to 10. That is, the support bearing 20 has an inner ring 32 having an inner ring raceway on its outer circumferential surface, an outer ring 33 having an outer ring raceway on its inner circumferential surface, and a plurality of balls 34, each of which is a rolling element, arranged between the inner ring raceway and the outer ring raceway. However, when implementing the present invention, a cylindrical roller bearing in which the rolling elements are cylindrical rollers, a tapered roller bearing in which the rolling elements are tapered rollers, or the like can also be used as the support bearing.

[0057] In this example, the inner ring 32 is fitted by an interference fit onto the large diameter cylindrical surface portion 31, which is the outer circumferential surface of the tip end portion of the worm 18. That is, the inner ring 32 is fitted and fixed onto the large diameter cylindrical surface portion 31. However, when implementing the present invention, the inner ring can also be fitted onto the outer circumferential surface of the tip end portion of the worm by intermediate fitting or the like so as to prevent radial rattling.

[0058] In this embodiment, as shown in FIG. 5, a radial gap is provided between the outer peripheral surface of the outer ring 33 and the inner peripheral surface of the holder 19, and a cylindrical bush 43 is disposed therebetween. That is, in this embodiment, the outer ring 33 is fitted into the inner peripheral surface of the bush 43 by clearance fit, and the bush 43 is fitted into the inner peripheral surface of the holder 19 in a state in which radial displacement is prevented. The bush 43 is a member for ensuring cushioning for the outer peripheral surface of the outer ring 33, that is, for suppressing impact and hitting noise when the outer peripheral surface of the outer ring 33 hits something. Such a bush 43 is preferably made of synthetic resin, rubber, or the like. When implementing the present invention, the bush may be omitted.

[0059] In this example, the tip of the worm 18 is capable of displacement in the second direction, which is the biasing direction of the leaf spring 21, based on the annular gap that exists between the outer peripheral surface of the outer ring 33 and the inner peripheral surface of the bush 43.

[0060] In this example, the bush 43 is fitted inside the inner peripheral surface of the holder tube portion 35 constituting the holder 19 by, for example, press fitting in a state in which radial displacement is prevented, and is fitted outside the outer peripheral surface of the outer ring 33 with a radial gap therebetween. A side surface on one side in the first direction of the bush 43 abuts against a side surface on the other side in the first direction of the holder side plate portion 38 constituting the holder 19. In addition, in the illustrated example, the bush 43 has a flange portion 44 that protrudes radially outward from an end portion on the other side in the first direction over the entire circumference. A side surface on one side in the first direction of the flange portion 44 abuts against a side surface on the other side in the first direction of the holder tube portion 35. However, the flange portion 44 may be omitted. The inner diameter of the bush 43 is approximately the same as the inner diameter of the holder side plate portion 38 constituting the holder 19. The bushing 43 has a protrusion 45 at one circumferential location on the outer circumferential surface, and the circumferential position of the bushing 43 relative to the holder 19 is regulated by engaging the protrusion 45 with the recess 37 of the holder 19. The bushing 43 has a notch 46 that opens radially inward and on both axial sides at a location axially opposing (aligning) with the notch 39 of the holder 19.

[0061] As shown in Figures 5, 6, and 9, the leaf spring 21 has a main body plate portion 47 attached to the spring retaining portion 36 and positioned on one side of the support bearing 20 in the first direction, and a pressing plate portion 48 connected to the main body plate portion 47 and pressing a portion of the outer peripheral surface of the outer ring 33 that is located farther from the worm wheel 17 in the second direction based on the elasticity generated in the main body plate portion 47.

[0062] When carrying out the present invention, the main body plate portion constituting the leaf spring can have any shape as long as it can generate elastic force for elastically biasing the tip end of the worm toward the worm wheel via the support bearing. In this example, the main body plate portion 47 has a substantially arc shape when viewed from the first direction, as shown in FIG.

[0063] Specifically, the main body plate portion 47 has an arc portion 49, a first straight portion 50, a second straight portion 51, a third straight portion 52, and a fourth straight portion 53. The arc portion 49 constitutes a circumferential intermediate portion of the main body plate portion 47, and has an arc shape with one side in the third direction being convex when viewed from the first direction. The first straight portion 50 extends from a circumferential end portion of the arc portion 49 that is closer to the worm wheel 17 in the second direction toward the other side in the third direction. The second straight portion 51 extends from an end portion of the first straight portion 50 on the other side in the third direction toward a side farther from the worm wheel 17 in the second direction. The third straight portion 52 extends from an end portion of the second straight portion 51 on the side farther from the worm wheel 17 in the second direction toward one side in the third direction. The length of the third straight portion 52 is shorter than the length of the first straight portion 50. The fourth straight portion 53 extends from an end of the arc portion 49 that is farther from the worm wheel 17 in the second direction toward the other side in the third direction. When implementing the present invention, the portion corresponding to the second straight portion 51 in this example may be configured by a plate portion having an arc shape. Furthermore, the portions corresponding to the second straight portion 51 and the third straight portion 52 in this example may have any shape as long as the shape allows the leaf spring to be attached to the spring holding portion by being hooked onto the spring holding portion.

[0064] In this example, the pressing plate portion 48 extends from the end portion on the other side in the third direction of the fourth straight portion 53 toward the other side in the first direction. As shown in Fig. 5, the pressing plate portion 48 has a V-shape with an intermediate portion in the first direction located at the radially innermost position. The pressing plate portion 48 has a guide plate portion 54 at the end portion on the other side in the first direction that is inclined in a direction toward the radially outward direction toward the other side in the first direction.

[0065] In this example, the leaf spring 21 is attached to the spring holding part 36 by press-fitting the other end in the third direction of the circumferential end 42 of the partial cylindrical part 40 constituting the spring holding part 36 between the first straight part 50 and the third straight part 52 constituting the main body plate part 47, as shown in Fig. 6. In this state, a part of the arc part 49 constituting the leaf spring 21 is arranged along the radial outer surface of the partial cylindrical part 40 of the spring holding part 36. In this state, the pressing plate part 48 constituting the leaf spring 21 is arranged inside the notches 39, 46 of the holder 19 and the bush 43, and the intermediate part of the pressing plate part 48 in the first direction presses the part of the outer peripheral surface of the outer ring 33 located on the side farther from the worm wheel 17 in the second direction based on the elastic force generated by elastically deforming the main body plate part 47. That is, in this example, when the leaf spring 21 is attached to the spring holding portion 36 and the intermediate portion in the first direction of the pressing plate portion 48 of the leaf spring 21 is in contact with a portion of the outer peripheral surface of the outer ring 33 located farther from the worm wheel 17 in the second direction, the main plate portion 47 of the leaf spring 21 is elastically deformed so that the distance between the end portion close to the worm wheel 17 in the second direction and the end portion farther from the worm wheel 17 is expanded. Then, based on the elastic force generated by this elastic deformation, the intermediate portion in the first direction of the pressing plate portion 48 presses the portion of the outer peripheral surface of the outer ring 33 located farther from the worm wheel 17 in the second direction. As a result, the leaf spring 21 elastically biases the tip portion of the worm 18 toward the worm wheel 17 via the support bearing 20.

[0066] In addition, when implementing the present invention, it is preferable that the circumferential length of the main body plate portion constituting the leaf spring be set to a length of more than half a circumference in the circumferential direction of the support bearing, as in main body plate portion 47 in this example (see Figure 6), from the viewpoint of keeping the bending rigidity of the main body plate portion low and generating an appropriate elasticity.

[0067] When assembling the worm reducer 14 of this example, the bushing 43 is fitted into the holder cylindrical portion 35 of the holder 19, and the leaf spring 21 is attached to the spring holding portion 36 of the holder 19. Then, the support bearing 20 is inserted radially inside the bushing 43 and the pressing plate portion 48 of the leaf spring 21 from the other side in the first direction. At this time, the radially inner surface of the guide plate portion 54 of the leaf spring 21 can function as a guide surface for guiding the outer ring 33 when the support bearing 20 is inserted.

[0068] According to the worm reduction gear 14 of this embodiment, the following advantageous effects can be obtained.

[0069] There is no pad that is pressed against and makes sliding contact with the outer peripheral surface of the tip of the worm 18. The tip of the worm 18 is supported in a rolling manner by the support bearing 20, which is a rolling bearing. Therefore, the operating torque of the worm 18 can be suppressed.

[0070] The entire biasing leaf spring 21 is not disposed overlapping radially outward from the support bearing 20 fitted onto the tip end of the worm 18. In other words, only the pressing plate portion 48 constituting the leaf spring 21 is disposed overlapping radially outward from the support bearing 20, and the main plate portion 47 constituting the leaf spring 21 is disposed on one side in the first direction from the support bearing 20. Therefore, at the location where the leaf spring 21 is installed, it is possible to prevent the worm accommodating portion 23 of the housing 16 from becoming large in diameter.

[0071] Of leaf spring 21, main body plate portion 47, which is a portion that generates elastic force for biasing, is disposed on one side in the first direction relative to support bearing 20. This makes it possible to ensure a wide arrangement space for main body plate portion 47. This makes it easy to ensure the degree of freedom in designing leaf spring 21 including main body plate portion 47.

[0072] [Second Example of the Implementation Form] A second embodiment of the present invention will be described with reference to FIGS.

[0073] In the structure of this example, an assembly of the holder 19a, the support bearing 20, the leaf spring 21a, and the bush 43a is assembled between the outer peripheral surface of the tip of the worm 18a and the inner peripheral surface of the tip of the worm accommodating portion 23a in a direction opposite to that of the first example of the embodiment. Therefore, the spring holding portion 36a constituting the holder 19a and the main plate portion 47a constituting the leaf spring 21a are disposed on the base end side of the worm 18a (left side in FIG. 11) with respect to the support bearing 20. Accordingly, in the structure of this example, the axial dimensions of the tip of the worm 18a and the tip of the worm accommodating portion 23a, which are located to the right of the support bearing 20 in FIG. 11, are made shorter than those of the first example of the embodiment, and the worm reducer is made more compact in the first direction accordingly. In the structure of this example, one side in the first direction is the left side in FIG. 11, ie, the base end side of the worm 18a, and the other side in the first direction is the right side in FIG.

[0074] In this example, the spring holding portion 36a constituting the holder 19a has an arc shape as a whole when viewed from the first direction. The flange portion 41a constituting the spring holding portion 36a protrudes radially inward from one end of the partial cylindrical portion 40a in the first direction.

[0075] In this example, the flange portion 44 (see FIG. 5) of the bushing 43a is omitted.

[0076] In this example, the second straight portion 51a of the main body plate portion 47a constituting the leaf spring 21a is bent outward in the radial direction of the arc portion 49a from the circumferential end portion of the arc portion 49a that is closer to the worm wheel 17 in the second direction. The third straight portion 52a of the main body plate portion 47a is bent from the tip end portion of the second straight portion 51a toward the arc portion 49a in the third direction, and the third straight portion 52a of the main body plate portion 47a is bent from the tip end portion of the second straight portion 51a toward the arc portion 49a in the third direction. Close to The end of the second electrode is disposed substantially parallel to the end of the first electrode.

[0077] 12, the leaf spring 21a is attached to the spring retaining portion 36a by press-fitting a circumferential end portion of the partial cylindrical portion 40a constituting the spring retaining portion 36a, the circumferential end portion being closer to the worm wheel 17 in the second direction, between an end portion of the arc portion 49a constituting the main body plate portion 47a, the end portion being closer to the worm wheel 17 in the second direction, and a third straight portion 52a. In this state, a part of the arc portion 49a constituting the main body plate portion 47a is disposed along the radially inner surface of the partial cylindrical portion 40a constituting the spring retaining portion 36a.

[0078] In this example, the pressing plate portion 48a constituting the leaf spring 21a does not include a guide plate portion 54 (see FIG. 5). Instead, the leaf spring 21a has a guide plate portion 54a extending to one side in the first direction from the tip end of the fourth straight portion 53 constituting the main body plate portion 47a. The guide plate portion 54a is inclined in a direction toward the radially outward direction as it approaches one side in the first direction.

[0079] When assembling the worm reduction gear of this embodiment, the holder tubular portion 3 of the holder 19a is to 5 After fitting the bush 43a and attaching the leaf spring 21a to the spring holding portion 36a of the holder 19a, the support bearing 20 is inserted from one side in the first direction radially inside the bush 43a and the pressing plate portion 48a of the leaf spring 21a. At this time, the radially inner surface of the guide plate portion 54a of the leaf spring 21a can function as a guide surface for guiding the outer ring 33 when the support bearing 20 is inserted. The other configurations and effects are similar to those of the first embodiment.

[0080] [Third Example of the Implementation Form] A third embodiment of the present invention will be described with reference to FIGS.

[0081] In the structure of this example, the bush 43b has bush spring portions 55, each of which has a smaller radial thickness than the adjacent portions on both sides in the circumferential direction, at two circumferential locations located on both sides in the third direction, each of which is adjacent to the outer ring 33 of the support bearing 20 in the third direction. In this example, the bush spring portions 55 are configured in a partially cylindrical shape with the radially outer side being a concave side and the radially inner side being a convex side.

[0082] In this example, the radially inner side surfaces of each of the two bushing spring portions 55 are in contact with the outer peripheral surface of the outer ring 33 of the support bearing 20. Also, the radially outer side surfaces of each of the two bushing spring portions 55 face the inner peripheral surface of the holder cylindrical portion 35 via a gap. In other words, a gap is provided on the radially outer side of each of the two bushing spring portions 55 to allow the bushing spring portions 55 to elastically deform radially outward.

[0083] In the structure of this example, regardless of the presence of a radial gap between the outer peripheral surface of the outer ring 33 and the inner peripheral surface of the bush 43b, the elasticity of the two bush spring parts 55 can prevent the tip of the worm from displacing in the third direction. When implementing the present invention, the number of bush spring parts can be one or three or more as long as the bush spring parts can prevent the tip of the worm from displacing in the third direction. When implementing the present invention, the bush can be molded integrally with the holder. In this case, a recess can be provided on the outer peripheral surface of the holder to form a gap that allows the bush spring parts to elastically deform radially outward. The other configurations and effects are similar to those of the second embodiment.

[0084] [Fourth Example of the Implementation Form] A fourth embodiment of the present invention will be described with reference to FIGS.

[0085] The worm reducer of this example further includes a second leaf spring 56 for suppressing displacement of the tip of the worm in the third direction relative to the holder 19a. In this example, the second leaf spring 56 is configured in a partially cylindrical shape as a whole, as shown in Fig. 18, and has a base portion 57 and two elastic plate portions 58.

[0086] The base portion 57 has an outer diameter side flat plate portion 59, an inner diameter side flat plate portion 60, and a connecting plate portion 61, which are arranged in a U-shape. The two elastic plate portions 58 extend in opposite directions to each other in the circumferential direction from both ends in the width direction of the inner diameter side flat plate portion 60. That is, each of the two elastic plate portions 58 is configured in a partial cylindrical shape.

[0087] 17, the second leaf spring 56 is attached to the holder tube portion 35 and the bush 43a such that the ends of the holder tube portion 35 and the bush 43a that are closer to the worm wheel 17 in the second direction are sandwiched between the outer diameter side flat plate portion 59 and the inner diameter side flat plate portion 60. In this state, the inner diameter side flat plate portion 60 and the two elastic plate portions 58 are disposed in a radial gap that exists between the outer peripheral surface of the outer ring 33 and the inner peripheral surface of the bush 43a, and the two elastic plate portions 58 elastically sandwich the outer ring 33 from both sides in the third direction.

[0088] In the structure of this example, regardless of the presence of a radial gap between the outer peripheral surface of the outer ring 33 and the inner peripheral surface of the bush 43a, the elasticity of the two elastic plate portions 58 can prevent the tip of the worm from displacing in the third direction. The other configurations and effects are similar to those of the second embodiment.

[0089] The present invention can be implemented by appropriately combining the configurations of the above-described embodiments to the extent that no contradiction occurs. [Explanation of symbols]

[0090] 1. Electric power steering device 2 Steering wheel 3 Steering shaft 4. Steering column 5a, 5b Universal joint 6 Intermediate shaft 7 Steering gear unit 8 Electrically assisted devices 9 Pinion shaft 10 Rack axis 11. Housing 12 Rack storage area 13 Pinion housing 14 Worm reducer 15 Electric motor 16 Housing 17 Worm Wheel 18, 18a Warm 19, 19a Holder 20 Support bearing 21, 21a Leaf spring 22 Wheel storage section 23 Worm housing 24 Wheel Teeth 25 worm teeth 26 Output shaft 27 Female spline part 28 Male spline part 29 Ball bearings 30 Small diameter cylindrical surface section 31 Large diameter cylindrical surface 32 Inner Circle 33 Outer Ring 34 balls 35 Holder tube 36, 36a Spring retainer 37 Recess 38 Holder side plate 39 Cutout 40, 40a Partial cylindrical portion 41, 41a Tsuba 42 Circumferential end 43, 43a Bush 44 Tsuba 45 Convex 46 Cutout 47, 47a Body plate 48, 48a Pressing plate part 49, 49a Arc section 50 1st straight section 51, 51a 2nd straight section 52, 52a 3rd straight section 53 4th straight line section 54, 54a Guide plate part 55 Bush spring part 56 Second leaf spring 57 Base 58 Elastic plate 59 Outer diameter side flat plate part 60 Inner diameter flat plate part 61 Connecting plate part 100 Worm reducer 101 Housing 102 Worm Wheel 103 Warm 104 Wheel storage section 105 Worm housing 106 Wheel Teeth 107 Rotational Axis 108 worm teeth 109a, 109b ball bearing 110 Holder 111 Large diameter section 112 Bush 113 Electric Motor 114 Pad 115 Torsion coil spring

Claims

1. a housing having a wheel accommodating portion and a worm accommodating portion whose axially intermediate portion is open to the wheel accommodating portion; A worm wheel having wheel teeth on an outer circumferential surface and rotatably supported inside the wheel accommodating portion; a worm having worm teeth on an outer circumferential surface thereof that mesh with the wheel teeth and that is rotatably supported inside the worm accommodating portion; a holder having an annular shape, a radially inner side of which is inserted a tip end of the worm, and which is fitted and fixed to the worm accommodating portion; a support bearing which is a rolling bearing and has an inner ring and an outer ring, and is disposed between an outer peripheral surface of a tip end of the worm and an inner peripheral surface of the holder with a radial gap being interposed between an outer peripheral surface of the outer ring and an inner peripheral surface of the holder; a leaf spring that is assembled to the holder and elastically biases the tip end of the worm toward the worm wheel via the support bearing, The holder has a holder tubular portion in which the support bearing is disposed on a radially inner side, and a spring retaining portion disposed adjacent to one side of the holder tubular portion in a first direction which is an axial direction of the worm accommodating portion, The leaf spring has a main body plate portion attached to the spring holding portion and disposed on one side of the support bearing in the first direction, and a pressing plate portion connected to the main body plate portion and pressing a portion of the outer peripheral surface of the outer ring that is located farther from the worm wheel in a second direction, which is a biasing direction of the tip portion of the worm by the leaf spring, based on elasticity generated by the main body plate portion. Worm reducer.

2. 2. The worm reducer according to claim 1, further comprising a cylindrical bushing that is fitted into the inner circumferential surface of the holder tube portion in a state in which radial displacement is prevented, and that is fitted into the outer circumferential surface of the outer ring with a radial gap therebetween.

3. 3. The worm reducer according to claim 2, wherein the bush has a bush spring portion, at a portion adjacent to the outer ring in a third direction perpendicular to both the first direction and the second direction, the bush having a smaller radial thickness than adjacent portions on both circumferential sides, the radially inner surface of the bush spring portion is in contact with the outer peripheral surface of the outer ring, and a gap is present radially outwardly of the bush spring portion, allowing the bush spring portion to elastically deform radially outward.

4. 4. The worm reduction gear according to claim 1, wherein one side in the first direction is a base end side of the worm.

5. a second leaf spring for suppressing displacement of the tip portion of the worm relative to the holder in a third direction perpendicular to both the first direction and the second direction, The second leaf spring has two elastic plate portions that elastically sandwich the outer ring from both sides in the third direction.

5. A worm reduction gear according to claim 1, 2 or 4.

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